Heat transmission units of the above type are used e.g. for the cooling of exhaust gases in an exhaust-gas recirculation line of an internal combustion engine. In such an arrangement, the ribs normally extend into the channel conducting the fluid which is to be cooled. In this regard, there exist variants wherein the ribs extend into the channel from both of the opposite sides of the heat transmission unit, as well as variants wherein the ribs extend into the channel only from one side. The ribs can have various shapes and they can extend as one-pieced ribs along the main flow direction or be formed as individual ribs; known ribs include pin- and tube-shaped ribs as well as airfoil-shaped ribs.
The channel conducting the coolant can be arranged within the fluid-conducting channel, or it can surround the fluid-conducting channel when seen in cross section.
In internal combustion machines, heat transmission units are used for the cooling of e.g. air, exhaust gas or lubricating oil. Thus, for instance, charge-air coolers are used for cooling the combustion temperatures and thus also the resultant nitrogen oxides, and exhaust-gas coolers are used for heating the air in order to warm up an occupant cell more quickly, or they are used in the exhaust-gas line in order to reduce the exhaust-gas temperature of a gas flowing towards a catalyst. In exhaust-gas recirculation lines, the exhaust-gas temperatures and thus the combustion temperature in the engine are reduced with the aid of the exhaust-gas cooler, which in turn will allow for a reduction of pollutant emissions. In each of the above cases, the cooling water of the internal combustion engine can serve as a coolant.
A heat transmission unit arranged in an exhaust-gas recirculation system of an internal combustion engine is known e.g. from DE 10 2004 019 554 A1. This unit comprises a channel conducting the exhaust gas along a U-shaped path and being surrounded along its whole cross section by a coolant-conducting channel. This known heat transmission unit is a multi-part pressure-gas cooler with several planes of division.
In such heat exchange units, there are desired both a high efficiency with respect to the heat which is to be transmitted, as well as a lowest possible sooting. At the same time, it is desired that the pressure loss via the heat transmission units be kept as low as possible.
The known heat transmission units, particularly in case of small throughputs and temperature differences, have merely low cooling performances and cooling efficiencies. Particularly in the region of exhaust-gas recirculation, however, it can be desirable—for further reduction of pollutant emissions—to obtain a high cooling performance with low pressure loss in cases of large throughputs and small throughputs alike.
Thus, it is an object of the invention to provide a heat transmission unit by which, while keeping the pressure loss at a minimum, high cooling performances and respectively cooling efficiencies can be obtained over a large range of throughputs and temperatures.